Every year, the world faces huge losses in lives and property due to residential and commercial fires caused by, electrical wiring. Human lives can be lost due to high temperature flames, toxic smoke and gas that are generated from the flammable insulation materials used in wires and cables during fire.
The current population uses various gadget and equipments that contain several wires and cables. Most wires and cables are fabricated from plastic materials that are readily flammable. However, modern living involves heavy use of electric equipment containing wires and communication systems made of cables. In addition, nowadays many people live and work in densely populated buildings and structures in limited spaces. These conditions further increase the mortality rate and property damage due to electrical fire stemming from bad wire or cable insulation. At the least smoke and toxic fumes emanating from poorly insulated materials in wires and cables can cause irreparable health damage and even loss of life.
Wire and cable insulations must meet both electrical properties and mechanical properties requirements. Polyethylene and polyvinylchloride compounds are some of the best materials for wire and cable insulations because of their excellent electrical and mechanical properties. However, these materials have major weaknesses due to their lack of flame retardancy and high generation of toxic gases.
Polyethylene, for example, is easily flammable but generates less toxic gases during burning. Conversely, Polyvinylchloride compound generates a high level of toxic gases even though it has acceptable flame retardancy. Current investigations are being carried out to find flame retardant materials for wires and cables that do not generate toxic gases, such as halogen free flame retardant compounds (HFFR compounds), clean flame retardant materials or non toxic flame retardant materials. Currently, clean flame retardant materials are made from special formulations based on halogen and toxicity free chemicals that restrict the generation of toxic smoke. Clean flame retardant materials mainly consist of matrix polymers that do not contain halogen, main flame retardants, secondary flame retardants, intumescent flame retardants, processing aids and antioxidants. (Mans V et al. 1998, Rai M et al. 1998, Wei P et al. 2006 and Luciana R et al. 2005). This resultant mixture has very poor mechanical properties.
Another significant problem with commercial clean materials is their unstable mechanical properties in spite of possessing high flame retardancy due to high filler loadings. Clean flame retardant materials contain relatively high content of flame retardants which are mainly consisted of inorganic materials. In general, high loadings of flame retardants are needed to achieve commercially acceptable flame retardancy for wire and cable applications. However, high levels of flame retardants lead to significant deterioration in mechanical properties. The insulation and jacket materials for wire and cable should meet appropriate tensile strength, elongation at break, thermal resistance and flame retardancy for proper use. Modified thermoplastic compound for wire and cable insulations must meet IEC 60502 and BS 6724 and 7655 standard requirements.
EVA(ethylene vinyl acetate), EVA/LDPE (low density polyethylene)(or LLDPE (linear LDPE), ethylene alpha olefin or ethylene ethyl acrylate are widely used as matrix polymer for their high flame retardant quality, load ability which can increase the flame retardancy. These polymers may be used in higher concentrations to improve flame retardancy. Inorganic materials, such as, aluminum trihydroixide (ATH), magnesium hydroxide (MH) and huntite hydromagnesite (HH) are used as flame retardants because of their high decomposition temperature and smoke suppression capabilities as clean flame retardant materials. However, more than 50% w/w of inorganic materials is sufficient for flame retardancy. High concentration of these flame retardants may lead to interfacial problems between matrix polymer and flame retardants, which could result in poor mechanical properties of the insulation of wires and cables.
Various studies have been performed to improve mechanical properties and flame retardancy using encapsulated organic flame retardants (Chang et al. 2006, Du L et al. 2006, Liu Y et al. 2006), combination of hydrotalcite with two other flame retardants and organo-modified montmorillonite (Laoutid F et al. 2006, Ma H et al. 2006).
Encapsulated organic flame retardants enhance the interfacial adhesion with matrix polymers and lead to improved dispersion in comparison to untreated flame retardants. Hydrotalcite composites increase flame retardancy by releasing more gas compared to general flame retardants during fire. In addition, partial substitution of general flame retardants by organo-modified montmorillonite improves fire properties. Nevertheless, most of studies focus to improve flame retardancy. However, cost of production and performance of the final products needs to be considered.
However, most of wire and cable production specifications for clean flame retardant materials require not only excellent mechanical properties but also high flame retardant properties. The minimum requirement for tensile strength is 8.8 MPa and minimum elongation at break is 125% based on IEC 60502 and BS 6724, 7655 standards for thermoplastic compounds. Without meeting these two important properties, the clean flame retardant materials are not suitable for wire and cable insulation materials. There is a need to obtain a cable or wire insulation material that contains a clean flame retardant material and has superior mechanical properties and flame retardancy.